An image pick-up apparatus or an image acquisition apparatus, such as, for example, a camera, may include an auto focusing function to automatically focus on a subject for the convenience of user. The auto focusing function mainly uses a through the lens (TTL) auto focusing method which uses the light entering through a photographing lens. An auto focus module detects whether a subject is in focus using, for example, a contrast detection method or a phase difference detection method. In the TTL auto focusing method, a sub-mirror is typically used for guiding the light entering through the photographing lens to the auto focus module.
In general, an AF area which indicates an area measurable by the auto focus module is smaller than the image pick-up area. This is mainly because the size of the sub-mirror is geometrically limited. Enlarging the AF area is a subject currently under study.
The manufacturing and/or assembly imprecision, which may in some cases be within the allowable tolerance, during the fabrication and/or assembly of the optical components in the image pick-up apparatus may result in an auto focusing error. An image pick-up apparatus of a robust design that is as impervious to the manufacturing and/or assembly tolerance as practicable may thus be desired.
An auto focus module adds to the size of the image pick-up apparatus, which size may be an important consideration for a consumer when making a purchasing decision. A reduction in size of the auto focus module may thus also be desirable.